Heat Transfer In Turbine Mid Structures

Abstract

In order to estimate the life time of a cooled gas turbine component, knowledge of the heat transfer is essential in order to predict the material temperature. Usually, a gas turbine has a hot turbine structure in between the high and low pressure turbines, which here is called the Turbine Mid Structure (TMS). The TMS has a complex design consisting of a hot aerodynamic and a cold load carrying structure. The TMS is usually cooled in order to limit the material temperature. To understand the heat transfer and to predict the material temperature in a TMS, a numerical study is performed. The FLUENT CFD tools are used to study the external gas path as well as the internal cooling flows. The CFD tools are validated to different fundamental heat transfer correlations. This numerical method is applied to the external turbine duct flow in both 2D and 3D analyses. For the internal cooling flow investigation, a simplified configuration is studied for different inlet conditions. In order to predict the wall temperature, a conjugated CFD model is built and compared to the thin shell conduction capability in FLUENT. In general, the predicted heat transfer for the external duct flow is in reasonable agreement with standard heat transfer correlations. The flow and heat transfer in the turbine duct is very complex and highly three dimensional with regions of separated flow. The internal cooling flow is also highly complex, governed by the feeding system, is non-uniform and shows a very strong coupling between the velocity field, air and metal temperatures. It is very demanding to build a conjugated CFD model and to model a realistic seal leakage. The preferred method to obtain the wall temperatures is the thin shell method with convective boundary conditions.